The influence of environmental aspects in the variation of natural radioactivity levels in selected brazilian beach sand samples

Abstract

At beaches, environmental implications added to shoreline erosion and artificial interventions on native structure may alter the concentration of the natural radionuclides in certain regions of the coast. In this work, eleven locations at Camburi beach, known to be a naturally high background region, were studied in 2011. The influence of environmental aspects, as geology, average temperatures, variations of the height of the tides and the rainfall levels were related with the variation of 226Ra, 232Th and 40K activities concentrations, during the year 2011 and annual effective dose were evaluated from the 226Ra, 232Th and 40K sands activities concentrations. Sand samples were monthly collected during 2011, dried, sealed in standard 100 mL HPDE polyethylene flasks and measured by high resolution gamma spectrometry after a 4 weeks in-growth period. The results, considering samples gamma-rays self-attenuation, show activities concentrations in the range from 4 Bq kg-1 to 1380 Bq kg-1 for 226Ra, 9 Bq kg-1 to 7453 Bq kg-1 for 232Th, and 6 Bq kg-1 to 504 Bq kg-1 for 40K. The absorbed dose rate (D) in outdoor air values laid from 9 nGy.h-1 to 5160 nGy.h-1 .The annual effective dose values for the sand samples considering a daily exposure of 24 hours all year round laid from 0.05 mSv.y-1 to 31.64 mSv.y-1. The annual effective dose values for the sand samples considering daily exposure of one hour all year round laid from 0.002 mSv.y-1 to 1.318 mSv.y-1.The annual effective dose (E) for the beach collection points for a resident of Vitoria city, with one hour daily exposure all year round by collection point laid from 0.003 mSv.y-1 to 0.232 mSv.y-1. The annual effective dose (E) for the collection points from Camburi beach for a tourist with 8 hours daily exposure on january, july or both, laid from 0.004 mSv.y-1 to 0.446 mSv.y-1. For a resident of Vitoria city and for a tourist, in the conditions of exposure of this work, all values of E are lower than the limit of 1 mSv y-1, recommended for ICRP 60 for the general public. In some months of the year 2011, low average temperatures, low rainfall levels and low variations of the height of the tides can be related with high 226Ra, 232Th and 40K activities concentrations. In April and in October, high rainfall levels and high variations of the height of the tides can be related with low 226Ra, 232Th and 40K activities concentrations.